Comparison of iron(III) and aluminum in precipitation of phosphate from solution

The results of phosphate precipitation using iron(III) (Hsu, 1973a) and aluminum (Hsu, 1975) are compared. It is suggested that these two coagulants react with phosphate following the same mechanism. The observed differences in optimum conditions and effectiveness of phosphate precipitation are interpreted by assuming that Fe3+ has a stronger affinity for PO43− and a stronger hydrolyzing power than Al3+.